The UV-absorbers have long been known as effective light stabilizers for organic materials and have enjoyed considerable commercial success. Among the commercial classes of chromophores are the oxanilides, the o-hydroxybenzophenones, the benzalmalonates, the cyanocinnamates and the hydroxyphenylbenzotriazoles.
However, the hitherto known compounds have in some circumstances exhibited limited compatibility in certain substrates, and excessive tendency to exude, sublime and/or volatilize during processing of stabilized compositions into sheets, films, fibers or other pellicles when processing must be done at elevated temperatures. Likewise such compounds may also suffer undue loss by volatilization or sublimation from fabricated structures, particularly thin films or coatings, especially when subjected to elevated temperatures during use.
Attempts have been made to increase compatibility and to reduce volatilization loss by modifying the structure of the compounds. The preparation of bis-o-hydroxybenzophenones is described in U.S. Pat. No. 3,666,713.
To be successful a compound must exhibit an excellent combination of compatibility with and/or solubility in numerous polymeric substances along with superior resistance to loss from stabilized compositions during high temperature processing or in end use applications where coatings or films of the stabilized compositions are exposed even to ambient weathering and light exposures. While improvements have been noted over the years, experience has shown that state-of-the-art light stabilizers for coatings to be inadequate for new and more stringent requirements for durability under weathering conditions. New coatings formulations had to be developed to decrease the amount of air pollution by release of a solvent to the atmosphere. These "high solids" coatings formulation have a minimal amount of solvent and demand greater solubility from the light stabilizers.